The Peg-billed Finch, Acanthidops bairdi, is a passerine bird of modest size, measuring approximately 13.5 cm in length and weighing around 16 grams. It is characterized by its long tail and a unique, upturned bill with a black upper mandible and a contrasting yellow lower mandible.
Adult males of this species are cloaked in a sleek slate grey plumage, which lightens towards the belly. Females, on the other hand, are dressed in olive-brown with a paler underside, and their heads and upper backs are tinged with grey. They are adorned with bright cinnamon wing bars and buff supercilia. The juveniles resemble females but are paler with less pronounced wing bars.
The Peg-billed Finch is an uncommon resident of the mountainous regions, favoring the edges and clearings of montane forests, as well as scrubby second growth, bamboo clumps, and bushy pastures. It thrives from altitudes of 1500 meters up to the timberline and may descend to 1200 meters during the wet season.
This bird is endemic to the highlands of Costa Rica and western Panama, where it can be found in locations such as Cerro de la Muerte, particularly when the bamboo is in bloom.
The Peg-billed Finch is often observed alone, in pairs, or in small family groups. It may also join mixed-species feeding flocks alongside other small birds, such as warblers.
The finch communicates with a dry "pzeek" call. The male's song is a melodic composition of high whistled notes that culminate in a distinctive buzz, rendered as "chee shee shee shee paah."
The female is solely responsible for constructing the nest, a cup-shaped structure made of plant material. She typically lays a clutch of four eggs and incubates them for a period of 12 to 14 days until they hatch.
The diet of the Peg-billed Finch is varied, including insects and spiders, as well as grass and bamboo seeds. Additionally, it has been observed extracting nectar from flowers and juice from berries.
The IUCN Red List currently classifies the Peg-billed Finch as Least Concern, indicating that, at present, there are no immediate threats to its population numbers that would warrant a higher risk category.